California is courting sovereign wealth funds, pensions and endowments for more than $50 billion to build Gov. Jerry Brown’s proposed bullet train to link the state’s largest cities, the most expensive public works project in U.S. history.

High-speed rail ventures such as California’s, which has weathered management shake-ups and fluctuating cost estimates, pose attractive opportunities for such investors, who together have $6 trillion in assets, said Andy Kunz, president and CEO of the U.S. High Speed Rail Association, a non-profit advocacy group meeting this week in Los Angeles.

California is the only U.S. state working to lay tracks for trains running as fast as 220 mph. The $68.4 billion project, linking San Francisco with Los Angeles, is counting on $10 billion in bonds authorized by voters, $3.3 billion committed by the federal government and as much as $55.1 billion from private sources.

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“We have active interest in and outreach to sovereign funds and foreign consortia that are looking at us,” Jeffrey Morales, CEO of the California High-Speed Rail Authority, said last week.

In addition to sovereign wealth funds, or state-owned investment pools, other potential investors include companies that will build and operate trains and stations, Mr. Morales said.

“Pension funds are definitely a potential investor,” Mr. Morales said. “They have been increasingly looking at infrastructure as an investment opportunity.”

Public works projects have become more attractive to investors seeking stable, if modest, returns in a volatile climate, said Bradley Morrow, a senior consultant for private markets at Towers Watson. “It’s becoming more accepted as an asset class for institutional investors in North America,” Mr. Morrow said, referring to a range of capital projects and not rail specifically.

California’s non-partisan Legislative Analyst’s Office labeled its state’s high-speed rail funding model “highly speculative” in April. In July, the Legislature voted to sell $2.6 billion in bonds approved by voters in 2008 toward the 800-mile project. However, lawmakers shelved Mr. Brown’s plan to earmark as much as $500 million a year in proceeds from auctioning tradeable carbon-emission permits.

Neither the $240.7 billion California Public Employees’ Retirement System, Sacramento, nor the $154.8 billion California State Teachers’ Retirement System, West Sacramento, has committed money to high-speed rail, according to spokesmen.

A spokesman for CalPERS, Joe DeAnda, and a spokesman for the teachers’ fund, Ricardo Duran, declined to comment on whether asset managers were considering high-speed rail, saying their funds don’t speculate on possible investments.